Transformer



Patented Mar. 2, 1943 TRANSFORMER Charles Philippe Boucher, Paterson, N.J., as-

signor to Boucher Inventions, Ltd., Washington, D. C., a corporation ofDelaware Application May 1, 1940, Serial No. 332,813

Claims.

This invention relates to negative load transformers and moreparticularly concerns transformers suitable for energizing luminousdisplay signs employing gaseous discharge tubes as the luminouselements.

One of the objects of my invention is t provide simple, practical andthoroughly reliable transformer apparatus which is well adapted towithstand the many varying conditions of load and whole or partialshort-circuit encountered in actual practical use. 1 Another object isthe provision of power transformer apparatus which is exceedinglycompact, highly efiicient and particularly economical in construction,installation and operation, enjoying low copper and iron losses, a highrate of heat dissipation and good operating power factor.

Still another object is to provide a transformer having shunt coremembers which can be manufactured inexpensively and which are sodesigned that after assembly the shunt paths of which they form partswill have the correct predetermined magnetic reluctances.

Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly consists in the combination of elements,features of construction and arrangement of parts, the scope of theapplication of which is indicated in the claims at the end of thespecification.

In the accompanying drawings, Figure 1 is a diagrammatic representationof a core-type transformer embodying certain features of my invention.

Figure 2 is a'sirnilar representation of a shell type transformer alsoembodying certain features of my invention.

Figure 3 is a detail View of one pair of the core shunt pieces used inthe transformer of Figure 2, showing the means for securing them inposition, and

Figure 4 is a side view of the parts shown in Figure 3.

Like reference characters denote like parts throughout the several viewsof the drawings.

As conducive to a more thorough understandin of my invention, it may benoted that in the operation of a luminescent sign employing one or moreluminescent gas filled tubes high potential electrical energy isrequired. The desired high potential electrical energy ordinarily issupplied by alternating current transformer apparatus connected to astandard single phase sixty cycle source at either one hundred and tenvolts or two hundred and twenty volts. The high potential electricalenergy has a maximum value of about In the operation of even a singleluminous sign or display, it often is necessary to use a plurality ofluminescent tubes. Since the maximum voltage to ground permitted by theFire Underwriters is approximately seven thousand five hundred volts,and consequently the maximum permissible voltage across any secondarycircuit is approximately fifteen thousand volts, tubes whose strikingpotential is in the neighborhood of fifteen thousand volts may not beconnected in a series circuit. Also, due to their different strikingpotentials and negative load operating characteristics they can not beoperated in a parallel circuit. Accordingly, each tube must have its ownseparate transformer secondary winding. In order to avoid the high costsof transformer equipment and installation which would be incurred inusing a separate transformer for each tube, transformers have beendesigned which have a plurality of secondary windings on one core.

In order that the current flowing through the secondary coil sections ofsuch transformers may not exceed a maximum safe value, the transformersare provided with magnetic by-passes including air gaps of highreluctance through which the major portion of the energizing flux isshunted when current is flowing through the secondary coil sections.These by-passes have, in the past, been formed in a number of differentmanners. My invention has as one of its objects the provision of shuntpaths which are so formed that many advantages are achieved in themanufacture and operation of the transformers in which they areincorporated.

In heretofore known and/or used multiple secondary circuit transformers,the shunt pieces have been formed either as integral parts of a core legor as parts separate from the main core. Where the shunt pieces areintegral parts of a core leg, their manufacture is expensive, because aspecial die must be used for each transformer having a different currentoutput. Likewise, the manufac-' ture of previously used shunt partswhich are separate from the main core, and of transformers in which suchparts are incorporated, has been attended with difficulties. This is dueto the fact that such parts have been assembled in such a manner thatthe butt joint formed between the part and the-main core was parallel tothe flat surfaces of the air gap. Thus, when heavy pressure was appliedin order to secure a good butt joint, the length of the air gap wasvaried enough to make accurate control of the shunt path reluctancedifficult, if not impossible. Moreover, a special die was necessary foreach shunt part designed for a secondary of different current output.That was true because the part had to be varied in width or length inorder to vary the reluctance of the air gap.

It is a further object of my invention, there fore, to provide amultiple secondary. circuit transformer whose magnetic shunt parts maybe made inexpensively, without requiring a new die for each transformerof different current output and yet which shunt parts will providemagnetic by-passes of the proper reluctance for all transformers ofnearly the same rating in which they are used. Moreover, it is my aim toprovide a transformer in which the reluctances of the magnetic shuntpaths can be accurately controlled.

Referring now to the practice of my invention and directing attention toFigure 1, it will be seen that my transformer consists of a corecomprising two legs II] and I I interconnected at their ends by membersI2 and I3. Primary coil section P is mounted on the leg II! and extendsover substantially the entire length of that leg. Secondary coilsections S1, S2, S3 and S4 are mounted on the leg II. The core membersare preferably formed of laminated magnetic steel and they are heldtogether by core bands I4 and I5, which are preferably of magneticmaterial. The core also includes a T-shaped shunt member I6 abutting theleg I I at about its midpoint and two L- shaped shunt members I! and I8which abut the leg II on opposite sides of its midpoint. The secondarycoil sections are mounted on the leg II in such a manner that a separatemagnetic shunt path is formed around each coil section by the T-shapedmember I6 and/or one of the L-shaped members I! and I8. The L-shapedmember II extends closely toward but does not abut the leg I2,forming'therewith an air gap G1 of high magnetic reluctance. Similarlyair gaps G2 and G3 are formed between the T-shaped member I6 and theL-shaped members I1 and I8 respectively, and air gap G4 is formedbetween L-shaped member I8 and the leg I3. Where the secondary coilsections S1, S2, S3 and S4 are of like current and voltage ratings, theair gaps G1, G2, G3 and G4 have equal reluctances. This conditionnormally obtains where the loads of the coils are substantially equal.On the other hand, where the loads are unequal and the current andvoltage demands on the secondary coils vary accordingly the air gaps areadjusted so that the power delivered by each coil section willcorrespond to the need of its load.

The manner of securing the members I6, I1, and

I8 in place is not shown in Figure l but is similar to that which willbe described later in connection with Figures 3 and 4. Like the maincore members, the shunt members are preferably made of laminatedmagnetic steel.

The primary coil P is energized through leads I9 and from a suitablesource of alternating current electrical energy 2|, such as a standardsingle-phase GO-cycle source of supply at 110 volts. As the current inthe coil P rises and falls between a maximum positive and a maximumnegative value in conformity with the alternations of the electromotiveforce impressed across its terminals, an alternating magnetomotive forceis induced in the transformer core. This magnetomotive force cause therise and fall of a magnetic flux which traverses the core and links thecoil sections of the secondary windings.

The coil sections comprising one secondary winding have their oneterminals grounded, the grounded terminals preferably being those whosegrounding places the coils in series, their other terminals beingconnected across the load of the winding. With this arrangement, thevoltage across the load is approximately double that across theterminals of any one coil section and yet the voltage to ground at nopoint exceeds the maximum safe value approved by the fire underwriters,Thus the coils S1 and S2 have their one terminals grounded to the coreat. 22 and 23 and their other terminals are connected across a negativeload, such as the fluorescent luminous tube T1. illustrated, by theleads 24 and 25. Similarly the one terminals of the coils S3 and S4 aregrounded to the core at 25 and 21 and their other terminals areconnected across the terminals of the luminescent tube T2 by the leads28 and 29. The core itself is preferably connected to ground, as at 30.

The transformer preferably is enclosed in a casing 3| having a cover 32.A suitable way of supporting the transformer in the casing is by restingit on the bases 33 and 36, the bases in turn resting on the bottom ofthe casing. The casing preferably is then filledwith an insulatingcompound to prevent the destructive effects of moisture and ozone on thecore and coils.

As the flux induced in the main core by the flow of current in primarycoil P rises and falls in value, electromotive forces are induced in thesecondary coils. When the potential across the terminals of the tube T1is sufiicient to ionize the gas therein, a current at once flows throughthe tube and its winding, which ,comprises coils S1 and S2. The currentflowing through coils S1 and S2 sets up a magnetomotive force whichopposes the coursing of the main flux. Accompanying this backmagnetomotive force, a portion of the main flux is diverted around thecoils S1 and S2 through a magnetic shunt path of high reluctance.Assuming that the flux is coursing in the direction of the arrows, asseen in Figure 1, that is, in a clockwise direction, at the moment underdiscussion, this shunt path will be from the leg I0 through leg I2, airgap G1, L-shaped member I'I, air gap G2, T-shaped member I6, leg II andleg I3, back to leg I0 when the tube T2 is not-operating. All the mainflux will still link the coil sections S: and S4 at this time.Similarly, when tube T2 becomes ionized, but tube T1 has not yet becomeionized, the main portion of the main flux will be diverted through ashunt path through leg III, leg I2, leg

II, T-shaped member I6, air gap Ge, L-shaped member I8, air gap G4, andleg I3, back to leg I0. Thus the main flux will still be linking thecoil sections S1 and S2. -When both tubes become I ionized, the majorportion of the main'flux will comes grounded. Such a condition may becaused byithe formation of a conductive fllm of moisture, atmosphericimpurities, matted insect bodies, tube load or between terminals and agrounded part of the system. When such a condition exists,

and the like between the terminals of the From an inspection OI Figure 1it will be apparent that it is a very simple matter to vary the lengthsof the air gaps. The legs I! and I3 and the members It, I l, and I8 canbe moved either to the right or to the left a suflicient amount to varythe reluctances of the air gaps the operation of my transformer will bethe same as that obtaining when the load is ionized and conductive whileoperating normally. Thus, if the tube T1 is grounded, the currentinduced in its secondary coil sections S1 and S: will generate a backmagnetomotive force opposing the coursing of the main flux and causingit to seek a path of high reluctance shunt path, including leg l2, airgap G1, member l1, gap G2, member l6 and leg H. Excessive current willtherefore not be generated in the coil sections S and S2 and overheatingof thesecoil sections, with consequent destruction of their insulation,will be prevented. The shunt construction provided for the coil;sections S3 and S4 will likewise protect those coil sections fromexcessive current, and consequent overheating, if the winding which theyform becomes grounded.

Where one winding becomes open-circuited, as for example, by thebreakage of the tube or tubes in its load, the other winding willcontinue to operate normally. Thus, if the tube T1 becomes broken, nocurrent will flow in the coils S1 and S2 comprising its secondarywinding. The main through the magnetic flux will continue to link thosecoils and also the coils S3 and S4 until the tube T2 becomes ionized, asin normal operation. A similar condition will obtain if it is the tubeT2 which breaks, the other tube T1 continuing to operate normally.

Where one of the coil sections becomes opencircuited, its whole windingwill of course be inoperative but the other winding will continue tooperate in a normal manner as is more particularly described in thepreceding paragraph.

Should one coil, say the coil S1, become grounded, its winding will berenderedinoperative but no dangerous condition of excessive currentflowing through it will exist, and the other winding will continue tooperate in a normal I manner. The voltage induced in the other coil S:will be insuflicient to ionize the gas in the tube coil S2. The currentin the grounded coil S1 will not reach an excessive value because acounter T1, hence no current will flow in tube T1, or the other coilsections and prevent an excessive shortcircuit current from flowing inthem should they become grounded. In fact, in my transformer theshort-circuit current is about the same as the normal load current.

' It will be understood that the operation of my transformer under thevarious conditions enumerated above will be the same during the otherhalf cycle of the impressed electromotive force. The flux will then becoursing in a direction opposite to that indicated by the arrows, butthe paths it follows will be identical for the same condition ofoperation. Due to persistence of vision, the luminescent tubes, whichare rendered ionized and luminous 120 times a second where a cyclesource of electromotive force is used, will appear to'be continuallylighted.

G1, G2, G3, and G4 as desired. Because of this, it is not necessary thatmembers It, I! and I8 be made to different sizes for transformers ofdifferent ratings. For this reason, different dies are not needed formanufacturing the shunt parts for different transformers and thus anitem of expense in manufacture is eliminated.

It will further be observed that in forming a tight butt joint betweenthe members It, I1, and I8 and the leg H, the reluctance of the air gapsG1, G2, G3 and G4 is not varied since the force exerted to move theshunt members firmly against leg II is applied in a direction parallelto the surfaces of-the air gap faces. The force used for this purpose isordinarily between ten and forty tons and is necessary to crush theburrs of the laminations, the small imperfections due to cutting anddirt particles on the joint surface. Where the ordinary type of shuntpart is used, the length of the air gap is frequently varied as much as0.005 inch and its reluctance is changed accordingly. In practicalconstruction and operation this constancy of airgap in spite ofdifferences in securing the shunt members is an exceedingly importantfactor. It assures controlled operation of the transformer.

My transformer has also many advantages in operation. A shunt path isprovided for each secondary coil section, so that danger of overheatingany coil section is avoided. Flexibility is thus achieved since anygrouping of secondary coil sections is possible without danger of overheating. A high degree of efficiency is achieved since the fluxby-passed around each secondary coil when there is current flowingthrough it nevertheless continues to link the as yet unoperated coilsections.

It will be understood that my transformer is capable of being modifiedin various ways. Thus, where the load of each secondary winding isrounded at its mid-point, the coil sections may be connected inopposition, a. complete circuit being formed between each half of theload and the corresponding coil section. With such a connection, thegrounding or open-circuiting of one coil section or of the half of theload corresponding to one coil section will not render the other coilsection and its half of the load inoperative. With the coils connectedin opposition, however, the maximum potential'diiference available forenergizing a load is about seven thousand five hundred volts. Only tubeswhich are half or less than half the size of the largest tubesenergizable by a series circuit can be used in such a circuit.

Also, as has been previously indicated, the coil sections may beconnected in any grouping. Thus coil S1 may be grouped with coil S4 andcoils S2 and S3 may be united to form the two secondary windings.

air-gaps are adjusted to vary the reluctance of the shunt paths inaccordance with the relative operating voltages of the various secondarycoils. Thus, if the tube T1 has a higher voltage rating than the tubeT2, the series-connected coil sections S1 and S2 will have a greaternumber of turns than the coil sections S3 and S4 and will operate atcorrespondingly higher voltages. In order that sufficient voltage may beinduced in coil sections S1 and S2 to maintain the tube T1 in an ionizedcondition after it has struck and current is flowing through thecircuit, the air gaps G1 and G2 are adjusted so as to have a higherreluctance than the gaps G3 and G4. As has already been indicated, thisis merely a matter of changing the relative positions of leg i2 andshunt members l1 and 16 to increase the lengths of air-gaps.

Considering now another embodiment of my invention, attention isdirected to Figure 2 in which I have shown a shell type transformerembodying my invention. The transformer comprises a core with primaryand secondary windings mounted-on the core. The core comprises outerlegs 35 and 36 and a centrally disposed core leg 31 parallel to theouter legs. Between the ends of the leg 35 and the ends of leg 31 areinterposed short bars 38 and 39. Likewise, short bars 40 and 4| arepositioned between the ends of leg 36 and the ends of leg 31. The partsare held in firmly abutting relationship by the core bands 43 and 42.The core preferably is grounded as at 44. Magnetic shunt paths of highreluctance are formed by the L-shaped members 45- -46, 4148, 49-50, l52,53-54, and 5556, which are so disposed as to abut the central core leg31 at their one ends. Each L-shaped member extends around a secondarycoil section and forms an air-gap with one of the short bars 36, 39, 40,and 4| or with the adjacent L-shaped member. The air-gaps so formed areindicated by the reference characters G1, G2, G3, G4, G5, G6, G1, G8,G9, G10, G11 and G12, as shown in the drawings.

The members 45 and 41 may be placed in back to back relationship with aspace A separating them, as shown, or if desired, they may be made inone T-shaped integral piece, or the member 45 may be turned around sothat its tip will form an air gap with member 41. Likewise, the members46 and 48 may be in back to back relation ship and separated by a spaceB, as illustrated, or they may be integral, or member 46 may be turnedaround. Illustratively, the magnetic shunt pieces are secured to thecentral core leg 31 to insure silent operation in the manner shown inFigures 3 and 4. The shunt parts 55 and 56 illustrated are enclosed in ametal clamp 61, and insulating pad 68 being interposed between the clampand the shunt parts. Theclamp has two ears 69 and drilled to receive abolt 11. Washers 13 and 14 insulate the bolt head and the nut 12 fromthe ears 69 and 10. The nut 12 is turned until the clamp 61 holds theparts firmly together. It will be understood that any other suitablemanner of securing the shunt parts to the core may be employed, the oneshown being merely illustrative.

The primary winding consists of two elongated coil sections P1 and P2connected in series by a lead 51 and mounted on the legs 35 and 36respectively. These primary coils are energized from a' source ofalternating current electrical energy'58, such as a standard 110-voltSO-cycle source. through leads 59 and 60. The construction noted iscompact and assures excellent transference of heat produced underoperating conditions. Where desired, P1 and P2 may be connected inparallel.

Three secondary windings are formed by the coil sections S1, S2, S3, S4,S5, and S6, all of which are mounted on the central leg 31. Coils S1 andS11 connected together in series form one winding energizing the tube T1through leads 6| and 62. A second winding is formed by seriallyconnectedcoils S3 and S4 and energizes tube T2 through leads 63 and 64. The thirdwinding comprises series-connected coils S5 and Se and energizes tube T3through leads 65 and 65. The secondary coils are preferably grounded attheir interconnections. Where the load of a winding is grounded at itsmidpoint, however, the coils may be connected in opposition, a completecircuit than being formed including each half of the tube load and thecorresponding secondary coil.

When the transformer is used indoors, it need not be enclosed in acasing. In outdoor use, however, a casing is necessary. For the sake ofclarity in the drawing, none is shown in Figure 2, but a casing similarto the one shown in Figure 1 may be used where desired.

The operation of this transformer is similar to the operation of thetransformer of Figure 1 which has already been described, with theexception that two main magnetic paths are provided and there are twomagnetic shunt paths associated with each secondary coil section. Thus,assuming that the flux is coursing in the direction of the arrows, itwill consist of two parts going from the legs and 36 respectively,through the bars 38 and respectively, into the central leg 31, where thetwo parts unite and link the secondary coils. At the right hand end ofthe member 31 the flux separates into two parts again, traversing thebars 39 and 41, re-

spectively, and returning to the legs 35 and 36 respectively. In normaloperation, as the tube T1 becomes ionized and conductive due to therising of the electromotive force induced in its secondary Winding coilsections S1 and S2 under excitation of the primary winding by thepotential impressed across its terminals, a counter magnetomotive forceis generated by the current flowing in the coils S1 and S2. This forcesthe major portion of the main magnetic flux to seek a path of lessreluctance. Two such paths are provided, from the leg 35 through bar 38,airgap G1, L-shaped member 45, leg 31,'member 41, air-gap G3, member 49,member 31, and bar 39, back to leg 35, and from leg'36 through bar 40,air-gap G2, member 46, leg 31, member '48, air-gap G4, member 50, member31, and bar 4| back to leg 36. The flux at this time continues to linkthe other coil sections S3, S4, S5, and Se, but passes around the coilsS1 and S2 as outlined above, so that an excessive current does not flowin those coils. Similarly, the coil sections comprising the otherwindings will be bypassed when their loads are operating. Should all theloads be operative at the same time, the major portion of the main fiuxwill pass through two paths of high reluctance excluding the member 31and including all the L-shaped shunt members and their associatedair-gaps.

As explained more fully in connection with Figure 1, safe operation ofthe transformer will be assured under conditions of grounding oropen-circuiting of a whole secondary winding or of one coil section ofthat winding.

As in the transformer shown in Figure 1, the shunt then assemble theother parts about the leg 37.

Although I have illustrated a transformer hav-- ing three secondarycircuits, it is to he stood that any other reasonable number.

It will be comprising a T'-shaped magnetic shunt core portion and two ormore L-shaped magnetic shunt core portions abutting said main coreportion at 2. In electrical transformer apparatus of the characterdescribed, in combination, a primary winding, one or more secondarywindings each comprising two coil sections, a core interlinking saidprimary winding and secondary coil sections and including interiorlythereof L-shaped portions which form a one ends of each of said L-shapedportions, maintaining the same in abutting relation with a the mainportion of the magnetic flux.

3. In electrical transformer apparatus of the character described, incombination, a core type transformer core; an elongated primary windingmounted on one leg of said core; one or more cluded air-gap,

terminals grounded to place said coil sections and T-shaped magneticshunt parts, abutting a portion of the core and spaced between adjacentsecondary coil sections and extending substantially but not completelyaround said coil sections, thereby forming magnetic coil sections whenthey are operating under closed-circuit or short-circuit conditions.

4. A constant current transformer comprising, in combination, a mainmagnetic core portion, a primary winding mounted on said core portion, aplurality'of secondary coil sections mounted o said core portion,

and at least one other magnetic shunt portion abutting the main magneticcore and extending inwardly of the main magnetic core and around anothersecondary coil section and forming with the first-mentioned shunt -coreportion and the main magnetic core a magnetic CHARLES PHEIPPE BOUCHER.

